Department of Cellular Biology, Center for Tropical and Emerging Global Diseases (CTEGD), University of Georgiagrid.213876.9, Athens, Georgia, USA.
Infectious Diseases & Pathology Research Team, Houston Methodist Research Institute, Houston, Texas, USA.
mSphere. 2022 Jun 29;7(3):e0016022. doi: 10.1128/msphere.00160-22. Epub 2022 May 19.
The protozoan Toxoplasma gondii is a highly successful obligate intracellular parasite that, upon invasion of its host cell, releases an array of host-modulating protein effectors to counter host defenses and further its own replication and dissemination. Early studies investigating the impact of T. gondii infection on host cell function revealed that this parasite can force normally quiescent cells to activate their cell cycle program. Prior reports by two independent groups identified the dense granule protein effector HCE1/TEEGR as being solely responsible for driving host cell transcriptional changes through its direct interaction with the cyclin E regulatory complex DP1 and associated transcription factors. Our group independently identified HCE1/TEEGR through the presence of distinct repeated regions found in a number of host nuclear targeted parasite effectors and verified its central role in initiating host cell cycle changes. Additionally, we report here the time-resolved kinetics of host cell cycle transition in response to HCE1/TEEGR, using the fluorescence ubiquitination cell cycle indicator reporter line (FUCCI), and reveal the existence of a block in S-phase progression and host DNA synthesis in several cell lines commonly used in the study of T. gondii. Importantly, we have observed that this S-phase block is not due to additional dense granule effectors but rather is dependent on the host cell line background and contact inhibition status of the host monolayer . This work highlights intriguing differences in the host response to reprogramming by the parasite and raises interesting questions regarding how parasite effectors differentially manipulate the host cell depending on the or context. Toxoplasma gondii chronically infects approximately one-third of the global population and can produce severe pathology in immunologically immature or compromised individuals. During infection, this parasite releases numerous host-targeted effector proteins that can dramatically alter the expression of a variety of host genes. A better understanding of parasite effectors and their host targets has the potential to not only provide ways to control infection but also inform us about our own basic biology. One host pathway that has been known to be altered by T. gondii infection is the cell cycle, and prior reports have identified a parasite effector, known as HCE1/TEEGR, as being responsible. In this report, we further our understanding of the kinetics of cell cycle transition induced by this effector and show that the capacity of HCE1/TEEGR to induce host cell DNA synthesis is dependent on both the cell type and the status of contact inhibition.
刚地弓形虫是一种高度成功的专性细胞内寄生虫，在入侵宿主细胞后，会释放一系列宿主调节蛋白效应物，以对抗宿主防御并进一步促进自身的复制和传播。早期研究调查了弓形虫感染对宿主细胞功能的影响，结果表明，这种寄生虫可以迫使通常静止的细胞激活其细胞周期程序。两个独立的研究小组先前的报告确定致密颗粒蛋白效应物 HCE1/TEEGR 是通过与细胞周期蛋白 E 调节复合物 DP1 和相关转录因子的直接相互作用，唯一负责驱动宿主细胞转录变化的因子。我们的研究小组通过在许多宿主核靶向寄生虫效应物中发现的独特重复区域独立鉴定出 HCE1/TEEGR，并验证了其在启动宿主细胞周期变化中的核心作用。此外，我们在这里报告了使用荧光泛素化细胞周期指示剂报告线 (FUCCI) 响应 HCE1/TEEGR 时宿主细胞周期转变的时程动力学，并揭示了在几种常用于弓形虫研究的细胞系中存在 S 期进展和宿主 DNA 合成的阻滞。重要的是，我们观察到这种 S 期阻滞不是由于额外的致密颗粒效应物引起的，而是依赖于宿主细胞系背景和宿主单层的接触抑制状态。这项工作突出了寄生虫对宿主重新编程的反应中的有趣差异，并提出了关于寄生虫效应物如何根据宿主细胞背景和接触抑制状态的不同而差异地操纵宿主细胞的有趣问题。刚地弓形虫慢性感染全球人口的约三分之一，在免疫不成熟或受损的个体中可产生严重的病理。在感染过程中，这种寄生虫会释放许多针对宿主的效应蛋白，这些蛋白可以显著改变各种宿主基因的表达。更好地了解寄生虫效应物及其宿主靶标不仅有可能控制感染，还可以使我们了解自身的基本生物学。已知弓形虫感染会改变宿主细胞周期的一个途径，先前的报告已经确定了一种寄生虫效应物，称为 HCE1/TEEGR，是负责该途径的效应物。在本报告中，我们进一步了解了该效应物诱导细胞周期转变的动力学，并表明 HCE1/TEEGR 诱导宿主细胞 DNA 合成的能力既依赖于细胞类型又依赖于接触抑制状态。
